{In Archive {In Archive In Archive} RE:1-hr SO2Modeling Results of McElmo Creek Gas Plant Modeling Results of McElmo Creek Gas Plant Modeling Results of McElmo Creek Gas Plant 

Flare Stack 

Scott Bohning Scott Bohning to: thormel 01/31/2011 07:34 AM

Cc: pflynn, Andrew Chew

Archive: This message is being viewed in an archive .

Tom -

Utah's inventory may well be enough, but I do not what geographic coverage it has, also major vs. minor 

sources... default is to look 50 km out from signifiant impact area around the source (more distant minor 

sources could be omitted). That would have overlap with Navajo Nation land, for which Utah may not 

have a lot of information. Either way, it would be good to have some "due diligence" assessment of what's 

it in the area, i.e. some corroboration from other sources of information, as a check.

- Scott B.

"Tom Hormel" Scott, 01/28/2011 08:28:50 AM

From: "Tom Hormel" <thormel@mcvehil-monnett.com>

To: Scott Bohning/R9/USEPA/US@EPA

Cc: <pflynn@rnrc.net>

Date: 01/28/2011 08:28 AM

Subject: RE: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack

Scott,

Per my telephone message, I can proceed with the cumulative modeling. However, I want to confirm that

contacting the Utah Division of Air Quality to obtain an background SO2 emission inventory is sufficient for 

this modeling. If you have a preferential approach for compiling the background SO2 emission inventory 

that differs from my proposed approach, please let me know.

Thanks,

Thomas Hormel

McVehil-Monnett Associates, Inc.

Vice President & Sr. Project Manager

44 Inverness Drive East, Bldg C.

Englewood, CO 80112

303.790.1332

mcvehil-monnett.com

From: Bohning.Scott@epamail.epa.gov [mailto:Bohning.Scott@epamail.epa.gov] 

Sent: Thursday, January 27, 2011 5:23 PM

To: thormel@mcvehil-monnett.com

Cc: Chew.Andrew@epamail.epa.gov

Subject: RE: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack

Tom -

Again I apologize for the delay... I did finally get a chance to look some more at what you want on flare 
modeled parameters and the AERMOD output. Since the results are above the interim SO2 SIL of (about)

7.8 μg/m3, it indeed appears that cumulative modeling will be needed, including nearby sources. If you 

wish to discuss, I am free for a call most times during next week (but late mornings tend to be booked, 

also mid-afternoon Wed. and Thurs.).

- Scott B.

-- 

=+=+=+=+=+=+=+=+=+=+=+=+=+=+=

"Scott Bohning" <bohning.scott@epa.gov>

U.S. EPA Region 9, AIR-7

415/947-4127 fax-3579

From: "Tom Hormel" <thormel@mcvehil-monnett.com>

To: Scott Bohning/R9/USEPA/US@EPA

Date: 01/21/2011 08:47 AM

Subject: RE: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack

Scott,

 

I am resending the attachments from my last two e-mails so that they are not zipped.

 

Sorry about the inconvenience.

 

Thanks,

 

Tom Hormel

McVehil-Monnett Associates

(303) 790-1332, ext. 134

thormel@mcvehil-monnett.com

-----Original Message-----

From: Bohning.Scott@epamail.epa.gov [mailto:Bohning.Scott@epamail.epa.gov] 

Sent: Thursday, January 20, 2011 5:26 PM

To: thormel@mcvehil-monnett.com

Subject: Re: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack

Tom -

Sorry that I have not had time to do this justice, & I am out Fri. 1/2... I will have to think some more to 

confirm, but right now it seems to me that you could use AERMOD flat terrain only if terrain really is pretty 

flat. I'm assuming it is not, so you would be stuck with the higher, complex terrain values, adn the need for 

a background inventory.
- Scott B.

-- 

=+=+=+=+=+=+=+=+=+=+=+=+=+=+=

"Scott Bohning" <bohning.scott@epa.gov>

U.S. EPA Region 9, AIR-7

415/947-4127 fax-3579

P.S. On the attachment, I do have "Flare Stack Parameter Estimation.pdf" from 12/22, however, per note 

at end of this e-mail, perhaps you could resend your later attachment, but with Zip file(s) renamed to have 

different extension, like ".zi". 

( our e-mail system strips all incoming and outgoing ".zip" files on the dubious grounds that they may 

contain a virus!)

From: "Tom Hormel" <thormel@mcvehil-monnett.com>

To: Scott Bohning/R9/USEPA/US@EPA

Cc: <pflynn@rnrc.net>

Date: 01/17/2011 09:59 AM

Subject: 1-hr SO2 Modeling Results of McElmo Creek Gas Plant Flare Stack

Scott,

Per my telephone message to you this morning, below is a copy of our 12/22/10 e-mail to you discussing

initial AERMOD modeling results for 1-hour SO2 impacts from McElmo Creek Gas Plant's flare stack. 

Please review so we can discuss these results and proceed with any additional modeling that may be 

required. The two files referenced in the 12/22 e-mail are attached for your convenience.

We look forward to your response.

Thanks,

Thomas Hormel

McVehil-Monnett Associates, Inc.

Vice President & Sr. Project Manager

44 Inverness Drive East, Bldg C.

Englewood, CO 80112

303.790.1332

mcvehil-monnett.com

E-mail from December 22, 2010, 3:29 PM MST

Scott,
We have modeled the flare stack at the McElmo Creek Gas Plant near Aneth, UT, using the AERMOD as 

we discussed recently. The flare stack was characterized as a point source by estimating effective stack 

diameter and stack height with stack velocity and temperature set at values consistent with SCREEN3 

guidance. The flare stack was modeled at four flare gas heat content values (i.e., 300, 443. 538.8 and 

682.4 BTU/SCF) with a constant SO2 emission rate based on 700 ppmv H2S. The modeled stack 

parameters and emission rate for each of these four flare gas heat content cases is summarized in the

attached table. The SCREEN3 output from the modeling report submitted in 2008 is also attached to 

show the consistency between the model input for AERMOD and the previous SCREEN3 modeling.

We ran the AERMOD both in the flat and complex terrain modes and get mixed results when comparing 

the maximum modeled 1-hour SO2 impacts to the 1 hour SO2 SIL of 7.9 ug/m^3. These modeling 

results are:

1. In the flat terrain mode, maximum 1--hour SO2 impacts are below the 1-hour SO2 SIL for the 443, 

538.8 and 682.8 BTU/SCF cases, but slightly over for the 300 BTU/SCF case (i.e., 8.5 vs. 7.9 ug/m^3)

2. In the complex terrain mode, maximum 1-hour SO2 impacts are above the 1-hour SO2 SIL for the 

300, 433 and 538.8 BTU/SCF cases and slightly below for the 682.4 BTU/SCF case; the highest 

maximum 1-hour SO2 impact is 22 ug/m^3 for the 300 BTU/SCF case and drops down to 15 ug/m^3 for 

the 433 BTU/SCF case.

If we rely on the flat terrain mode runs which would be consistent with the simple terrain assumed for the 

2008 SCREEN3 modeling, we demonstrate modeled 1-hour SO2 impacts below the SIL by citing the 

results for the three higher heat content cases. Recent monthly flare gas analysis data suggest that the 

lowest heat content of the flare gas is approximately 500 BTU/SCF and that the 300 BTU/SCF is an 

unrealistically conservative case. However, if we rely on the complex terrain results, regional modeling 

with background SO2 emission sources may be necessary because of the results described above.

We would like to discuss these modeled impacts to determine if we need to pursue getting a background 

SO2 emission inventory at your convenience.

Thank you for your assistance,

Tom Hormel

McVehil-Monnett Associates

(303) 790-1332, ext. 134

thormel@mcvehil-monnett.com

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[attachment "Flare Stack Parameter Estimation_122010.xls" deleted by Scott 

Bohning/R9/USEPA/US] [attachment "SCREEN3 SO2 Runs_2008.pdf" deleted by Scott 

Bohning/R9/USEPA/US] [attachment "AERMOD Results_1 hr SO2.pdf" deleted by Scott 

Bohning/R9/USEPA/US]